1. Field of the Invention
The present invention provides ultra-intense laser pulses capable of interacting with matter, and more specifically, it relates to a system and a method of lengthening a pulse""s duration by distributing its spectral content in space prior to or after amplification to produce a high power, short pulse. The distribution of the spectral content in space results in a chirped beam.
2. Description of Related Art
The conventional method for circumventing optical damage due to amplification of high intensity pulsed sources is accomplished by chirped-pulse amplification (i.e., CPA).
Chirped pulse amplification had its origin during microwave radar development more than 50 years ago. In the optical case, one avoids intensity dependent damage by increasing the input temporal pulse duration prior to amplification by passing an input pulse through a frequency dependent delay line. A chirped pulse in time is produced wherein the instantaneous frequency varies linearly as a function of time. A CPA system typically includes a pulse source and an optical pulse stretcher and compressor comprised of diffraction gratings to manipulate the frequency components of a received ultra-short pulse. In the pulse-stretching phase, components manipulate the optical frequencies of a received ultra-short pulse to form a temporal duration that can be amplified by a laser gain medium without initiating optically induced damage that would otherwise occur if the temporal properties of the pulse were left unchanged. Normally, after reaching a desired amplification, a compressor (i.e., conventionally a pair of parallel diffraction gratings) reverses the optical paths of the frequency components to reproduce the original temporal duration of the input pulse source.
Accordingly, the present invention provides a short pulse laser system that uses dispersive optics in a chirped-beam amplification system to produce high peak power pulses without the potential for intensity dependent damage to an amplifier or final optics after amplification.
Another aspect of the present invention provides a short pulse laser system that uses dispersive optics in a chirped-beam amplification system to produce high peak power pulses without the potential for intensity dependent damage to an amplifier or final optics after amplification or wherein the dispersive optics in a chirped-beam amplification system are adapted to receive amplified temporally chirped pulses prior to producing a chirped beam to enable high peak power pulses without the potential for intensity dependent damage to an amplifier or final optics.
The present invention incorporates a laser source having an output bandwidth capable of generating high power pulses using the technique of chirped-beam amplification. The present invention includes a pair of diffraction gratings that disperses one or more positive temporally chirped pulses from a lasing source and collimates the spectral content of the dispersed pulse(s) to produce a chirped i beam. An amplifying laser material having a gain bandwidth and a saturation fluence necessary to amplify the bandwidth of the laser source is positioned after the diffraction gratings to amplify the chirped beam to a predetermined energy. A refractive or reflective optic then focuses the amplified chirped beam to a rapidly longitudinally varying temporal and intensity confocal region to produce a high-energy pulse of short duration.
A method of the present invention includes the steps of producing optically chirped pulses having a predetermined spectral content, dispersing the pulses by utilizing dispersive optics to spread the spectral content of the chirped pulses spatially, collimating the spectral content to produce pulses having long local temporal durations in a chirped beam, wherein the ratio of input and output beam dimensions produces a predetermined spatial chirp ratio, between about 2 and about 100, amplifying the output beam received from the final dispersive optic, and compressing the amplified beam in time and space.
An additional method aspect provides for xe2x80x9cChirped Pulse Juxtaposed with Beam Amplification,xe2x80x9d wherein a chirped pulse amplification (CPA) design precedes a chirped beam amplification (CBA) arrangement to further extend the local pulse duration to provide high peak powers.
Accordingly, the present chirped-beam amplification apparatus and method provides for an efficient, cost effective arrangement, capable of high peak powers (an intensity greater than 1012 Watts, with pulse-widths less than 2.5 ps). The present system and method is useful for ultra-high precision laser machining, ultra-high resolution multiphoton microscopy, and the system""s increased longitudinal intensity localization can play a role in new pondermotive particle acceleration schemes.